The suspect in the triple slaying at a Starbucks coffee house in the District was not pressured or coerced into making statements and voluntarily admitted to the killings after his arrest in March, three police detectives testified yesterday.

Carl Derek Cooper was given plenty of food and rest and treated fairly during the 80 hours he was in the custody of the FBI and Prince George's County police, the investigators said. They challenged assertions by Cooper's attorneys that he lied about his role in the July 1997 crime because he was under extreme duress.

"He was willing to talk to us, anxious to talk to us, most of the time he was with us," said Detective Troy Hardin, of the Prince George's police.

Hardin and two colleagues testified yesterday at a hearing in U.S. District Court in Washington to determine whether Cooper's statements can be admitted as evidence in his trial April 10 on murder, racketeering and other charges. Cooper's attorneys want those statements barred, arguing that authorities violated his constitutional rights during four days of marathon interrogation.

The outcome could be critical to the prosecution. Authorities have not recovered the weapons used in the Starbucks slayings and have no fingerprints to connect Cooper to the crime scene, just north of Georgetown. One of his statements vividly describes the killings of Starbucks employees Mary Caitrin Mahoney, 25, Emory Allen Evans, 25, and Aaron David Goodrich, 18. The proceedings are scheduled to resume Tuesday.

Cooper, 30, was the prime suspect when he was arrested March 1, 1999, at his Northeast Washington home. Although he initially was charged with the 1996 shooting of an off-duty Prince George's County police officer, authorities were eager to question him about the Starbucks case and posed questions to him at the FBI's Washington field office and at Prince George's police headquarters.

After more than six hours of questioning by the FBI, Cooper was taken to D.C. Superior Court, where he waived extradition to Prince George's to face charges in the shooting of the off-duty officer. His court-appointed attorney said then that Cooper was invoking his right to remain silent and to have an attorney.

But Richard Fulginiti, a Prince George's detective, said Cooper wanted to resume talking about Starbucks as soon as he left the District.

Cooper was advised of his rights repeatedly and signed seven forms over the next few days agreeing to talk without an attorney, according to authorities. He signed the statements and most of his account was provided in his own handwriting, detectives said.

Prince George's Sgt. Joe McCann testified that Cooper was alert, focused and at ease, even after he took responsibility for the killings. "It was almost like a sense of final relief, as if now this monkey was off his back," McCann testified.

CAPTION: Carl Derek Cooper is trying to prevent statements he made to police from being used at trial.